Organic light-emitting diodes (referred to as OLEDs hereinafter) have advantages such as self-emission, high contrast, high luminance, wide viewing angle and fast response, and thus have been widely used in displays. As compared to a conventional single OLED unit, a tandem OLED, which consists of two or more OLED units connected in series, may achieve the same luminance as that of the conventional single OLED unit at a relatively low current density, and thus has a relatively long service life. In addition, the colors of lights emitted by the respective OLED units of the tandem OLED may be adjusted individually, and thus the tandem OLED is suitable for emitting white light.
The tandem OLED includes a p-type carrier generation layer for generating holes. It is disclosed, for example, in J. Mater. Chem., 2011, 21, pp. 15332-15336, that a thiophene derivative is used for forming the p-type carrier generation layer of the tandem OLED. However, few literature has discussed in detail materials that can serve as the p-type carrier generation layer of the tandem OLED and how such materials can be used to modify the luminance, the external quantum efficiency, the current efficiency and the like of the tandem OLED.
Therefore, there is still a need in the art to develop a novel compound for the p-type carrier generation layer of the tandem OLED in order to enhance the luminance, the external quantum efficiency, the current efficiency and the like of the tandem OLED as compared to the conventional single OLED unit.